A Vasopressin-like peptide in the medicinal leech, Hirudo medicinalis

Arginine-vasopressin (AVP) is a member of the oxytocin/vasopressin family, which are structurally related nonapeptides. A VP-immunoreactivity (A VPD was localized to a set of neurons in the central nervous system (CNS) of the medicinal leech using hnrnunocytochemistry. Although the general staining pattern in the midbody ganglia is confined to 5 bilateral pairs of neurons, there are variations to this immunoreactivity. Of particular interest is a pair of immunoreactive neurons in the head brain area that based on anatomy could be classified as projection neurons. The A VPI seems to be confined to the CNS. Attempts at isolating the immunoreactive substance from the nerve cord extract through SDS-PAGE and western immunoblot analysis were unsuccessful probably due to the small molecular size of the peptide. Bath-application of 104 - 1 o-s M concentrations of synthetic A VP caused a highly pronounced hyperpolarization effect in the heart excitatory (HE) motor neurons in 100% of the experiments performed. Further analysis revealed that A VP is not affecting the heart central pattern generators and is modifying the HE neurons directly. In 60% of the current injection studies we observed a change in the membrane properties ofthe HE cells indicative of ion channels opening. Since this second effect far outlasted the hyperpolarization effect, it seems that A VP might have two independent effects on the HE motor neurons. In addition, due to the long period of time required for the onset of the effect to occur, we believe that A VP is acting through a modulatory synapse. These findings extend the oxytocin/vasopressin-like peptides in the annelid phylum to include Hirudo medicinalis. Item only available to the CSUSM community. Authentication with campus user name and password required.